Registering middleware in Laravel - Step-by-Step Execution

Concept Flow - Registering middleware

Create Middleware Class

↓

Add Middleware to Kernel

↓

Assign Middleware to Route or Group

↓

Request Hits Route

↓

Middleware Executes

↓

Request Proceeds or Blocked

Middleware is created, registered in the kernel, assigned to routes, then runs on requests to control access or modify requests.

Execution Sample

Laravel

<?php
// In app/Http/Kernel.php
protected $routeMiddleware = [
    'auth' => \App\Http\Middleware\Authenticate::class,
];

This code registers the 'auth' middleware by linking its name to the middleware class in the Kernel.

Execution Table

Step	Action	Details	Result
1	Create Middleware Class	Generate middleware file with handle method	Middleware class ready
2	Register Middleware	Add middleware to $routeMiddleware in Kernel.php	'auth' key linked to Authenticate class
3	Assign Middleware	Use 'auth' in route or group middleware	Routes protected by auth middleware
4	Request Received	User sends request to protected route	Request enters middleware pipeline
5	Middleware Executes	Authenticate::handle checks user auth	Request allowed or redirected
6	Request Proceeds	If authenticated, request continues to controller	Controller processes request
7	Request Blocked	If not authenticated, middleware redirects	User sent to login page

💡 Execution stops when request is either allowed to proceed or redirected by middleware.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 5	Final
$routeMiddleware['auth']	undefined	\App\Http\Middleware\Authenticate::class	\App\Http\Middleware\Authenticate::class	Middleware instance	Middleware allows or blocks request
Request Status	New request	New request	Assigned to auth middleware	Checked authentication	Allowed or redirected

Key Moments - 3 Insights

Why do we add middleware to the Kernel before using it in routes?

Middleware must be registered in the Kernel's $routeMiddleware array so Laravel knows what class to run when the middleware name is used in routes. See execution_table step 2.

What happens if the middleware blocks the request?

If the middleware detects the user is not authenticated, it redirects the request (step 7), stopping it from reaching the controller. This prevents unauthorized access.

Can middleware be assigned to multiple routes?

Yes, once registered, the middleware name can be used on any route or group to protect multiple routes easily (step 3).

Visual Quiz - 3 Questions

Look at the execution_table, what is the result after step 2?

A Middleware redirects user

B 'auth' key linked to Authenticate class

C Request proceeds to controller

D Middleware class deleted

💡 Hint

Check the 'Result' column for step 2 in the execution_table.

At which step does the middleware check if the user is authenticated?

A Step 3

B Step 7

C Step 5

D Step 1

💡 Hint

Look for 'Authenticate::handle checks user auth' in the 'Details' column.

If middleware is not registered in the Kernel, what happens when used in a route?

A Laravel throws an error because it can't find the middleware class

B Middleware runs normally

C Request is always allowed

D Request is always blocked

💡 Hint

Think about the importance of step 2 in the execution_table.

Concept Snapshot

Register middleware by:
1. Creating middleware class with handle method.
2. Adding it to $routeMiddleware in app/Http/Kernel.php.
3. Using middleware name in routes or groups.
Middleware runs on requests to allow or block access.

Full Transcript

Registering middleware in Laravel involves creating a middleware class that contains logic to run on HTTP requests. This class is then registered in the app/Http/Kernel.php file inside the $routeMiddleware array, linking a short name like 'auth' to the middleware class. After registration, this middleware name can be assigned to routes or route groups to protect them. When a request hits a route with middleware, Laravel runs the middleware's handle method. The middleware can check conditions like user authentication and decide to allow the request to continue to the controller or redirect the user elsewhere. This process ensures controlled access and request modification in Laravel applications.

Practice

1. What is the main purpose of registering middleware in Laravel's Kernel.php file?

easy

A. To define database connections

B. To make middleware available for use in routes and controllers

C. To create new views

D. To register event listeners

Solution

1. Step 1: Understand middleware role

   Middleware acts as a filter for HTTP requests in Laravel.

2. Step 2: Purpose of registering middleware

   Registering middleware in Kernel.php makes it available to assign to routes or groups.

3. Final Answer:

   To make middleware available for use in routes and controllers -> Option B

4. Quick Check:

   Middleware registration = availability for routes [OK]

Hint: Middleware must be registered to use it in routes [OK]

Common Mistakes:

• Confusing middleware registration with database setup
• Thinking middleware creates views
• Mixing middleware with event listeners

2. Which of the following is the correct way to register a route middleware named checkAge in app/Http/Kernel.php?

easy

A. 'checkAge' => \App\Http\Middleware\CheckAge::class,

B. 'checkAge' => 'CheckAgeMiddleware',

C. 'checkAge' => new CheckAge(),

D. 'checkAge' => 'middleware.checkAge',

Solution

1. Step 1: Locate middleware registration syntax

   In Kernel.php, route middleware are registered as key-value pairs with the key as the name and value as the class reference.

2. Step 2: Match correct syntax

   The correct syntax uses the fully qualified class name with ::class keyword.

3. Final Answer:

   'checkAge' => \App\Http\Middleware\CheckAge::class, -> Option A

4. Quick Check:

   Middleware registration uses class reference [OK]

Hint: Use full class path with ::class to register middleware [OK]

Common Mistakes:

• Using string names instead of class references
• Instantiating middleware instead of referencing class
• Using incorrect keys or formats

3. Given the following Kernel.php snippet, what middleware will be applied when accessing the route /profile?

protected $routeMiddleware = [
    'auth' => \App\Http\Middleware\Authenticate::class,
    'verified' => \App\Http\Middleware\EnsureEmailIsVerified::class,
];

Route::middleware(['auth', 'verified'])->get('/profile', function () {
    return 'User Profile';
});

medium

A. Both 'auth' and 'verified' middleware run

B. Only the 'auth' middleware runs

C. No middleware runs

D. Only the 'verified' middleware runs

Solution

1. Step 1: Check middleware registration

   Both 'auth' and 'verified' middleware are registered in $routeMiddleware.

2. Step 2: Analyze route middleware assignment

   The route applies both middleware by listing them in the array ['auth', 'verified'].

3. Final Answer:

   Both 'auth' and 'verified' middleware run -> Option A

4. Quick Check:

   Route middleware array applies all listed middleware [OK]

Hint: All middleware in array run in order [OK]

Common Mistakes:

• Assuming only one middleware runs
• Confusing middleware registration with application
• Ignoring middleware order

4. Identify the error in this middleware registration snippet inside Kernel.php:

protected $routeMiddleware = [
    'admin' => App\Http\Middleware\AdminCheck,
];

medium

A. Middleware should be registered in $middleware property

B. Middleware name 'admin' is invalid

C. Missing the ::class keyword after the middleware class name

D. Namespace should not be used in Kernel.php

Solution

1. Step 1: Review middleware registration syntax

   Middleware classes must be referenced with the ::class keyword to provide the full class name as a string.

2. Step 2: Identify missing part

   The snippet misses ::class after App\Http\Middleware\AdminCheck.

3. Final Answer:

   Missing the ::class keyword after the middleware class name -> Option C

4. Quick Check:

   Middleware class references need ::class [OK]

Hint: Always add ::class after middleware class name [OK]

Common Mistakes:

• Omitting ::class causing syntax errors
• Registering middleware in wrong property
• Using invalid middleware names

5. You want to create a middleware that logs every request to a specific route group. After creating the middleware class, what is the correct way to register and apply it to the route group in Laravel?

hard

A. Use the middleware class name as a string in the route group without registration

B. Add the middleware class directly inside the route group without registration

C. Register the middleware in $middleware property and apply it only to the route group

D. Register the middleware in Kernel.php under $routeMiddleware with a name, then apply it in the route group using middleware('name')

Solution

1. Step 1: Register middleware properly

   Custom middleware must be registered in $routeMiddleware in Kernel.php with a key name.

2. Step 2: Apply middleware to route group

   Use the registered name in the route group with middleware('name') to apply it.

3. Final Answer:

   Register the middleware in Kernel.php under $routeMiddleware with a name, then apply it in the route group using middleware('name') -> Option D

4. Quick Check:

   Register then apply by name for route groups [OK]

Hint: Register middleware name, then use it in route groups [OK]

Common Mistakes:

• Skipping registration and using class name directly
• Registering middleware globally instead of route-specific
• Misplacing middleware registration property